We propose to assess the oncogenic risk of ultrasound, using the C3H/10T1/2 in vitro assay for malignant transformation. This assay is a more direct and quantitative measure of oncogenic risk than are assays of mutation or chromosomal alterations. Ultrasonic beams configured to simulate diagnostic and therapeutic conditions will be used to irradiate cells alone, in combination with carcinogenic treatment (2 Gy of 100-kVp X rays), or followed by post-treatment culturing in 0.1 Mug/ml of 12-0-tetradecanoyl-phorbol-13-acetate (TPA) in order to investigate the possible oncogenic interaction of co-stressors and tumor promotors with ultrasound. Experiments will be designed to detect a malignant transformation rate of 1x10 minus 4, equivalent to the response to 1 Gy of 100 kVp X-rays or to about 2 Mug/ml of benzo(a)pyrene. Cells will be irradiated at 1.7 MHz in suspension in a transmission chamber at 37 degrees C using uniform (unfocused) beam profiles, with irradiation times ranging from 1 to 10 minutes. Emphasis will be placed on providing replicable, well-characterized ultrasound delivery and bioassay.